1. Field of the Invention
The present invention relates generally to the field of casting products for orthopedic medicine and more specifically to the design of an improved casting method and apparatus for forming a hard structure about a body portion.
2. Background of Related Art Splints and medical casts are available for orthopedic purposes for the use in treatment of injuries to support and immobilize body portions. Typically, medical bandages are formed of a strip of fabric or scrim material impregnated with a substance which hardens into a rigid structure after the strip has been wrapped around a body member.
Traditionally, plaster of paris has been used as a hardening substance in fabricating a cast or splint upon an injured body portion. The cast is formed by initially applying a protective covering of a cotton fabric and then wrapping the body portion with a woven cloth impregnated with a plaster of paris which has been wetted by dipping in water immediately prior to application. Plaster of paris casts are widely utilized because of their low cost and their ability to conform to the contours of a body portion.
Plaster of paris casts, however, have a number of attendant disadvantages, including a low strength to weight ratio resulting in a cast which is bulky and heavy. In addition, plaster of paris casts develop their strength over an extended period of time, often requiring a period of 24 to 72 hours to develop full strength and therefore requiring the avoidance of weight bearing situations as the cast strengthens during this period. Plaster of paris casts also typically disintegrate in water, therefore making it necessary to avoid activities involving contact with water. Even if activities involving contact with water are avoided, perspiration over an extended period of time can break down the plaster of paris and create localized problems with odor and itching.
Plaster of paris casts also have numerous disadvantages related to the process of their fabrication. Specifically, the process of fabricating a plaster of paris cast is often very messy, time consuming, and requires multiple supplies and considerable skill. Wet casting material can get onto everything used in a casting environment from hands, clothes, patient, floor, furniture and the like.
In order to overcome the disadvantages of conventional plaster of paris casts, efforts have been made to provide a casting product having a plurality of layers of plaster of paris impregnated cloth. Such casting devices and methods of application thereof may enclose the casting material in sleeves or coverings of various materials so that direct contact with the casting material is not necessary (for example U.S. Pat. Nos. 4,235,228, 4,442,833, 4454,874 and 4,628,917). Some devices have attempted to provide measures which prevent moisture from the skin in the form of a moisture impervious layer next to the skin (U.S. Pat. No. 4,454,874). Other devices include a separate dry pad or layer which can be applied to the body portion after the casting material has been wetted (U.S. Pat. No. 4,628,917). Despite the noted efforts, plaster of paris casts still result in poor strength to weight ratios, and require an extended period of time to harden to full strength. Furthermore, even if wetting is avoided during the fabrication of the cast, perspiration over time may cause a breakdown in the plaster of paris or conversely if moisture impervious layers are used, such layers may restrict respiration.
An alternative to a plaster of paris cast is a synthetic cast which includes a flexible fabric impregnated with a curable resin that is hardened on the patient after the limb or body part to be splinted is wrapped with the fabric. Synthetic splints are generally lighter, more durable, and more water-resistant than plaster splints. However, resin used in synthetic splints is usually very sensitive to minute amounts of moisture and the resin can be activated simply by exposure to moisture in the atmosphere over a period of time.
Typically, synthetic splints are created from a resin impregnated fabric or substrate that is rolled into a coil and is dispensed from a dispensing box. Oftentimes, the impregnated substrate comprises woven fiberglass layers and is contained within a moisture impervious sleeve prior to use. In use, a portion of the resin impregnated substrate is separated from the coil and is exposed to water. The wetted impregnated substrate is then applied to a particular body portion. Before applying the resin impregnated substrate, however, a cushioning protective layer is generally disposed between the skin of the patient and the substrate.
During fabrication of a cast using the synthetic material, the resin can cause irritation to a patient because of migration of resin vapor and resin particles to the patients skin. In addition, fumes from the curing resin may cause irritation to the patient and individuals preparing the cast. Accordingly, there are environmental and health concerns related to the fabrication of synthetic casts not exhibited with plaster of paris casts. Another drawback in the utilization of woven fiberglass layers to form the substrate is that the hardened splint may not have consistent strength throughout all directions such that some fibers are more wetted than other fibers. Yet another drawback is that the thickness must be determined at the time of casting the splint and is not predetermined.
From the above discussion, it is readily apparent that both the traditional plaster of paris casting and the moisture-curable resin casting methods have advantages and disadvantages. On the one hand, plaster of paris casts are bulky, heavy in order to achieve the necessary strength, and difficult and messy to apply. On the other hand, moisture curable resins are very sensitive to the presence of moisture, the resin can cause sensory irritation to the patient and medical service providers, and the fiberglass may not have consistent strength due to inconsistent wetting of the resin.